The present invention relates to pressure sensors, and more, particularly, to thermoconductive vacuum pressure sensors.
Thermoconductive vacuum transducers (sensors) measure pressure by monitoring the temperature of a heated wire filament in the transducer as heat is transferred to the surrounding gas and case, in particular. The heat transferred and therefore the temperature of the filament will vary proportionally to the amount of gas pressure about the filament since the gas density is directly proportional to the pressure. The heated gas typically transfers the heat to the transducer wall or case. Two types of such transducers are the Pirani gage and the thermocouple gage which may have a thermopile therein. These transducers are physically large as compared to IC circuits and are thus not suited to uses where space is limited and other factors limit their application.
It is known to convert pressure signals into electrical signals by utilizing the piezoresistive effect of a semiconductor crystal. A conventional pressure sensor as a typical embodiment of this method has a silicon plate or block a portion of which takes the form of a diaphragm and a diffused resistor formed in a surface region of the silicon diaphragm. When there is a difference between the pressures on the two sides of the silicon diaphragm, the resistance of the diffused resistor varies proportionally to the magnitude of the pressure difference or to the resultant stress on the silicon diaphragm. It is clear that this apparatus has size limitations since one must have a moving diaphragm that is electrically isolated with the resistor therein.
Other types of pressure transducers are based upon changes in capacity of a flexing membrane.
The present invention is directed toward providing a solid state gas sensor having none of the above limitations.